Building walls, retaining walls and perimeter fence-type walls are often made with concrete block. These construction methods are easily done manually, but are time consuming and create a product that has many mortar joints, which are inherently weak. In cases where joints are eliminated by the use of concrete panels, the panels are often massive and require heavy machinery to assemble into the desired structure. If smaller panels are used, it is still necessary to incorporate structural reinforcement within the panel, complicating the panel manufacturing process. What is needed are improved precast concrete panel systems and constructions methods using precast concrete panels.